The present invention relates to semiconductor devices, and more particularly, to an internal voltage generation circuit for a semiconductor device which is capable of reducing unnecessary power consumption, and a method for generating an internal voltage therein.
Most semiconductor devices such as a dynamic random access memory (DRAM) devices include an internal voltage generation circuit inside a chip to supply voltages necessary for operation of internal circuits. The internal voltage generation circuit is a circuit for generating internal voltages of various levels by using an external power supply voltage (VDD) and a ground voltage (VSS). In designing the internal voltage generation circuit, a main issue is to stably supply an internal voltage having a desired level.
As semiconductor devices operate at higher speed, requirements for low power consumption are increasing and thus design techniques for meeting performance required at a low voltage environment are needed. In such a low power environment, most of semiconductor devices use a high voltage (VPP) having a voltage level higher than a power supply voltage (VDD) so as to compensate for a voltage loss generated when they operate at the power supply voltage (VDD) and to retain stable data.
Specifically, DRAM devices widely use a high voltage (VPP) for compensating for loss caused by a threshold voltage of a MOS transistor in a word line driver, a signal line separator, a data output buffer, and so on. In a DRAM, a back bias voltage (VBB) having a voltage level lower than the ground voltage (VSS) is applied to a bulk of an NMOS transistor used as a cell transistor. The high voltage (VPP) and the back bias voltage (VBB) are generated by a charge pumping operation. A high voltage (VPP) generator and a back bias voltage (VBB) generator have the same configuration because their voltage generation mechanisms are equal to each other.
FIG. 1 is a block diagram of a conventional internal voltage generation circuit of a semiconductor device. The conventional internal voltage generation circuit includes a voltage detecting unit 100, an oscillating unit 120, and a pumping unit 140. The voltage detecting unit 100 detects a voltage level of an internal voltage (VPP) output terminal to output a voltage detection signal DET. The oscillating unit 120 generates an oscillation signal OSC having a predefined frequency in response to the voltage detection signal DET. The pumping unit 140 performs a charge pumping operation in response to the oscillation signal OSC to output an internal voltage VPP to the internal voltage (VPP) output terminal.
The pumping unit 140 includes a pumping controller 142 and a charge pump 144. The pumping controller 142 generates a pumping control signal CTRL in response to the oscillation signal OSC. The charge pump 144 performs a charge pumping operation in response to the pumping control signal CTRL to output the internal voltage VPP to the internal voltage (VPP) output terminal.
Further, first to third drivers 160, 170 and 146 for driving output signals of the respective components are provided among the respective components of the internal voltage generation circuit; i.e., the voltage detecting unit 100, the oscillating unit 120, the pumping controller 142, and the charge pump 144. Each of the first to third drivers 160, 170 and 146 includes a plurality of inverters constructing inverter chains. An operation of the conventional internal voltage generation circuit will be described below.
The voltage detecting unit 100 generates the voltage detection signal DET by comparing a reference voltage VREF with the internal voltage VPP fed back from the internal voltage (VPP) output terminal of the pumping unit 140. The voltage detection signal DET is activated when the internal voltage VPP is lower than the reference voltage VREF, and it is deactivated when the internal voltage VPP is higher than the reference voltage VREF. An activation period of the voltage detection signal DET is changed according to the voltage level difference between the internal voltage VPP and the reference voltage VREF. The voltage detection signal DET has a long activation period when the voltage level difference between the internal voltage VPP and the reference voltage VREF is relatively great, and it has a short activation period when the voltage level difference between the internal voltage VPP and the reference voltage VREF is relatively small.
The first driver 160 is connected to a voltage detection signal (DET) output terminal. The first driver 160 maintains a phase and a logic level of the voltage detection signal DET as they are, and pulls up or pulls down the voltage level of the voltage detection signal DET, thereby preventing the voltage detection signal DET from being floated by noise.
The oscillating unit 120 generates the oscillation signal OSC having the predefined frequency in response to the voltage detection signal DET inputted from the voltage detecting unit 100. The oscillation signal OSC is oscillated at the predefined frequency when the voltage detection signal DET is activated. The oscillation signal OSC is maintained at a deactivated state, without being oscillated, when the voltage detection signal DET is deactivated. When the internal voltage VPP is lower than the reference voltage VREF, the oscillation signal OSC is oscillated at the predefined frequency. When the internal voltage VPP is higher than the reference voltage VREF, the oscillation signal OSC is maintained at a deactivated state, without being oscillated.
The second driver 170 is connected to an oscillation signal (OSC) output terminal. The second driver 170 maintains a phase and a logic level of the oscillation signal OSC as they are, and pulls up or pulls down the voltage level of the oscillation signal OSC, thereby preventing the oscillation signal OSC from being floated by noise.
When the oscillation signal OSC is oscillated at a predefined frequency, the pumping unit 140 performs a charge pumping operation to generate the internal voltage VPP. When the oscillation signal OSC is not oscillated and is in a deactivated state, the pumping unit 140 performs no charge pumping operation, so that the internal voltage VPP is not generated. When the internal voltage VPP is lower than the reference voltage VREF, the pumping unit 140 performs a charge pumping operation to generate the internal voltage VPP. When the internal voltage VPP is higher than the reference voltage VREF, the pumping unit 140 performs no charge pumping operation, so that the internal voltage VPP is not generated.
The pumping controller 142 of the pumping unit 140 generates the pumping control signal CTRL in response to the oscillation signal OSC. The pumping control signal CTRL is a signal for controlling the charge pumping operation of the charge pump 144. The pumping control signal CTRL is generated by changing the phase of the oscillation signal OSC. The pumping control signal CTRL may include multiple signals each having a different phase. The number and waveform of the pumping control signal CTRL may be changed according to the configuration of the charge pump 144 of the pumping unit 140.
Like the first and second drivers 160 and 170, the third driver 146 is connected to a pumping control signal (CTRL) output terminal. The third driver 146 maintains a phase and a logic level of the pumping control signal CTRL as they are, and pulls up or pulls down the voltage level of the pumping control signal CTRL, thereby preventing the pumping control signal CTRL from being floated by noise.
When a plurality of codes are included in the pumping control signal CTRL, the third driver 146 is provided in plurality. The third drivers 146 are connected to the plurality of codes of the pumping control signal CTRL in 1:1 correspondence.
The charge pump 144 performs a charge pumping operation in response to the pumping control signal CTRL to generate the internal voltage VPP. For example, when the pumping control signal CTRL is oscillated, the charge pump 144 performs a charge pumping operation to generate the internal voltage VPP. When the pumping control signal CTRL is not oscillated, the charge pump 144 performs no charge pumping operation, so that the internal voltage VPP is not generated.
In summary, when the internal voltage VPP is lower than the reference voltage VREF, the charge pumping operation is performed to increase the voltage level of the internal voltage VPP. On the other hand, when the voltage level of the internal voltage VPP is higher than the reference voltage VREF, the charge pumping operation is not performed until the voltage level of the internal voltage VPP becomes lower than a voltage level of the reference voltage VREF.
FIG. 2 is a timing diagram of the various signals in the conventional internal voltage generation circuit of FIG. 1. The voltage level of the internal voltage VPP repetitively rises and falls according to the voltage detection signal DET, and its variation width is relatively great.
More specifically, when the voltage detection signal DET is in a deactivated initial state of a logic high level, the oscillation signal OSC outputted from the oscillating unit 120 is not oscillated but maintained in a deactivated state of a logic low level. First to fourth codes, i.e., P1, P2, G1 and G2, included in the pumping control signals CTRL are also not oscillated but maintained in a deactivated state of a logic high or low level.
Therefore, the charge pump 144 does not perform a charge pumping operation, so that the voltage level of the internal voltage VPP falls. In the semiconductor device, the voltage level of the internal voltage VPP may fall due to a direct use or a natural discharge.
The voltage detection signal DET is activated when the voltage level of the internal voltage VPP becomes lower than a target level. When the voltage detection signal DET is activated to a logic low level, the oscillation signal OSC is oscillated at a predefined frequency and thus the first to fourth codes P1, P2, G1 and G2 are also oscillated at a predefined frequency.
The charge pump 144 performs a charge pumping operation to increase the voltage level of the increase voltage VPP. Thereafter, the voltage detection signal DET is deactivated when the voltage level of the internal voltage VPP sufficiently increases and becomes higher than the target level.
When the voltage detection signal DET is deactivated to a logic high level, the oscillation signal OSC is deactivated to a logic low level without being oscillated. Thus, the first to fourth codes P1, P2, G1 and G2 are deactivated to a logic high or low level without being oscillated.
In the conventional internal voltage generation circuit, the voltage detection signal DET is deactivated when the voltage level of the internal voltage VPP is higher than the voltage level of the reference voltage VREF and must pass through the oscillating unit 120 and the pumping controller 142, so that it can be transferred up to the charge pump 144 performing the actual charge pumping operation.
In this way, the voltage detecting unit 100 deactivates the activated voltage detection signal DET immediately when the voltage level of the internal voltage VPP reaches the target level. However, the charge pump 144 is controlled by the deactivated voltage detection signal DET passing through the oscillating unit 120 and the pumping controller 142. Therefore, the charge pump 144 continuously operates during a time period {circle around (1)} where the voltage detection signal DET passes through the oscillating unit 120 and the pumping controller 142, thereby increasing the voltage level of the internal voltage VPP.
If the charge pump 144 continuously operates during the time period {circle around (1)} where the voltage detection signal DET passes through the oscillating unit 120 and the pumping controller 142 even when the voltage level of the internal voltage VPP need not be increased, the voltage level of the internal voltage VPP excessively increases, causing malfunction of the semiconductor device.
Further, the oscillating unit 120, the pumping controller 142, and the charge pump 144 unnecessarily operate during the time period {circle around (1)} where the voltage detection signal DET passes through the oscillating unit 120 and the pumping controller 142 even when the voltage level of the internal voltage VPP need not be increased. Consequently, the semiconductor device unnecessarily consumes power due to the unnecessary operation.